1. Field of the Invention
The present invention relates to a hydraulic control device for valve trains of an engine.
2. Description of the Related Art
Among hybrid vehicles, a type of hybrid vehicle is known in which a cylinder deactivation operation is executed, for example, by controlling valve trains of an engine using hydraulic control method in order to further improve fuel economy by means of reduction in friction of the engine. In this type of hybrid vehicle, when the vehicle enters in a deceleration state, a cylinder deactivation operation is executed along with a fuel cut operation so as to decrease engine friction, and as a result, the amount of regenerated electric energy is increased by an amount corresponding to the decreased engine friction, and thus fuel economy is improved.
Accordingly, if an engine is employed, in which an all-cylinder deactivation operation is made possible, energy, which would have been dissipated due to engine friction during a deceleration operation, can be recovered to the maximum, and thus a hybrid vehicle having excellent fuel economy can be obtained.
As described above, fuel economy can be greatly improved using an all-cylinder deactivation operation; however, in general, some of the cylinders must remain as normally activated cylinders so as to be able to drive the vehicle just in case a cylinder deactivation mechanism fails, and at the same time, a motor of the vehicle cannot drive the vehicle. Accordingly, friction due to the normally activated cylinders remain unchanged during a deceleration operation; therefore, fuel economy is not greatly improved.